The present invention relates to a failsafe monitoring system for detecting actual or impending failure of a rupture disc and providing an alarm when such a failure occurs.
The most frequent utilization of a rupture disc is in pipelines which are normally unused vent passageways in a chemical process system but which are intended to provide safety relief should some process vessel or conduit over or under pressurize, thereby creating a hazardous condition. The rupture disc, by its nature, is usually hidden from view and, therefore, it is often difficult to visually determine when failure thereof has occurred. Even when it is obvious to an observer that failure of a rupture disc has occurred, such as when a gas or liquid fluid is suddenly venting or flowing into an open area where none should be, it is still important that the failure be noticed as quickly as possible, since the fluid may be hazardous and/or explosive, and since some type of safety equipment or procedure may be immediately required to protect personnel and/or equipment. For example, it may be necessary to shut off a pump to stop the discharge.
Conventional rupture disc alarm systems typically require that a portion of a broken disc engage a sensing probe or similar device before an alarm is sounded. A disc failure, however, can be sufficiently explosive or unpredictable in operation to leave no parts in position for engaging the probe or the probe itself can be rendered inoperative due to damage or electrical failure. Also, the probe systems typically do not detect potential failure of a disc, such as the stretching thereof to a predetermined percentage of the failure point. Further, conventional systems normally detect failure of a disc in only one direction, thus requiring multiple systems. Still further, probe systems are usually difficult to install and require special mounting parts and procedures. In addition, conventional alarm systems are often not failsafe, whereby they do not sound an alarm in case of part failure or loss of power.
It is noted that pressure switches have been utilized to sense failure of a rupture disc; however, such switches can only be used in closed systems wherein pressure will build downstream of a broken rupture disc and thus activate the switch, especially if the escaping fluid has a low pressure differential across the disc and slow flow rates. It is therefore desirous to have a failure sensing device which will function in open as well as closed systems and particularly in low pressures.
It is also noted that rupture discs are often used in areas wherein there is a potential for explosion. Therefore parts of a rupture disc in the explosive area should be intrinsically safe electrically and otherwise explosion proof.